Effect of Deposit Scale on Mechanical Properties of In-Situ Alloyed CrCoNi Medium Entropy Alloys Formed by Directed Energy Deposition.

Directed energy deposition (DED), as an additive manufacturing technology, has shown unique advantages in multi-material additive manufacturing and remanufacturing. In this study, two types in-situ alloyed CrCoNi medium entropy alloys that have thin-walled structures with different thicknesses (T1 and T2) were manufactured by the DED process, and the mechanisms of differences in relative density, microstructure, and mechanical properties at different heights were systematically analyzed. In terms of microstructure, the T1 and T2 samples along the building direction exhibit significant differences in crystallographic orientation, grain size, and dislocation density, which are related to the local temperature gradient differences caused by the scanning path and heat accumulation.

A facile strategy based on the metal-free design of carbon to deliver an insight into the active sites for liquid phase carbocatalysis.

An effective method to study the active sites for carbocatalysis is proposed based on designing a carbon catalyst in the absence of metal as the growth catalyst. The results suggest that the oxygenated groups on the aromatic carbons are mainly responsible for the catalytic reduction of nitrobenzene and some other reactions.

High Yield Controlled Synthesis of Nano-Graphene Oxide by Water Electrolytic Oxidation of Glassy Carbon for Metal-Free Catalysis.

The strong quantum confinement effect as well as abundant edges and oxygen functional groups enable nano-graphene oxide (NGO) a variety of intriguing applications such as catalysis, bioimaging, drug delivery and photovoltaic devices. However, the development of NGO is severely hindered because of the difficulty in controlled mass production. Here, we report the efficient synthesis of NGO with a high yield of ∼40 wt % by water electrolytic oxidation of glassy carbon (GC).

A comparative study of nitrobenzene reduction using model catalysts.

A zigzag-type quinone performs better than an armchair-type quinone in the reduction of nitrobenzene. When different kinds of functionalities co-exist, the reaction is dominated by the most active sites, but the most negative sites should also be taken into consideration if the acitive sites have zigzag structures.

Biomass-Derived Graphene-like Carbon: Efficient Metal-Free Carbocatalysts for Epoxidation.

N-doped graphene-like layered carbon (NG) could be synthesized via a metal-free pyrolysis route from glucose, fructose, and 5-hydroxymethylfurfural (5-HMF), which are cheap and widely available biomass or biomass derivatives. A well-developed thin-layer structure with large lateral dimensions could be obtained when 5-HMF was used as the precursor. More importantly, the 5-HMF-derived NG gave superior performance in epoxidation reactions compared with the conventional carbon catalysts and the performance of 5-HMF derived NG was even similar to that of a cobalt catalyst.

Hydrothermal Carbon Enriched with Oxygenated Groups from Biomass Glucose as an Efficient Carbocatalyst.

Metal-free carbocatalysts enriched with specific oxygenated groups with different morphology and size were synthesized from glucose by hydrothermal carbonization, in which cheap and widely available biomass could be converted into functionalized carbon using an environmentally benign process. The hydroxy- and carbonyl-enriched hydrothermal carbon (HTC) could be used in nitrobenzene reduction, and higher conversion was obtained on the sphere morphology with smaller size. In the Beckmann rearrangement of cyclohexanone oxime, carboxyl-enriched HTC exhibited superior performance compared with conventional solid acid (such as HY and HZSM-5), on which the strong acid sites and weak Lewis acid sites lead to high selectivity for the side product.

Carbocatalysis in Liquid-Phase Reactions.

There is broad interest in metal-free catalysis for sustainable chemistry. Carbocatalysis is a "green" option for catalytic transformations in the gas phase as well as in the liquid phase. This is evident by the numerous reports on gas-phase dehydrogenation and selective oxidation where carbon can be used as a successful alternative to metal oxide systems.

Active sites and mechanisms for direct oxidation of benzene to phenol over carbon catalysts.

The direct oxidation of benzene to phenol with H2 O2 as the oxidizer, which is regarded as an environmentally friendly process, can be efficiently catalyzed by carbon catalysts. However, the detailed roles of carbon catalysts, especially what is the active site, are still a topic of debate controversy. Herein, we present a fundamental consideration of possible mechanisms for this oxidation reaction by using small molecular model catalysts, Raman spectra, static secondary ion mass spectroscopy (SIMS), DFT calculations, quasi in situ ATR-IR and UV spectra.

Carbon nanotubes oxidized by a green method as efficient metal-free catalysts for nitroarene reduction.

Hydrogen peroxide (H2O2) functionalized carbon nanotubes exhibited better catalytic performance than their nitric acid oxidized counterparts in the reduction of nitrobenzene. One important reason may be attributed to the notably less negative oxygenated groups on the surface of the former one.

Mixed template effect adjusted by amine concentration in ionothermal synthesis of molecular sieves.

Cationic templating of imidazolium adjusted by the amine concentration in an ionothermal system results in products with larger channels or cage-like structures by reassembling the inorganic hosts around the changed organic guests.